1. Field of the Invention
The present invention relates to a solenoid control valve for a hydraulic engine valve actuator. More specifically, the present invention relates to a solenoid control valve for a hydraulic engine valve actuator using a coil induced electromagnetic field acting on an iron spool ring to translate a spool valve.
2. Description of the Prior Art
A major obstacle to the efficient operation of internal combustion engines has been the timing of the opening and closing of both the intake and the exhaust engine valves. In the ideal situation, both the timing and the lift of the engine valve can be independently regulated by an electronic control unit depending on the operational needs of the engine intake or exhaust. One method to provide for independent operation of the valves is through a hydraulic actuator where a high pressure hydraulic source is used to supply the energy to open and close the valve according to the position of a hydraulic control valve as determined by an electronic control unit. Prior art devices can be seen by reference to U.S. Pat. Nos. 3,926,159; 4,791,895; 4,930,464; 4,821,689; and 5,255,641 the disclosures of which are hereby expressly incorporated by reference.
To control the flow of hydraulic or engine oil through a hydraulic actuator, a solenoid valve is commonly used as disclosed, for example, in U.S. Pat. Nos. 4,957,075, 5,255,641 and 4,200,067 the disclosures of which are hereby expressly incorporated by reference. Solenoid valves are placed on each of the hydraulic lines to turn the flow on and off in response to electronic control signals.
One problem with the use of solenoid valves is that their actions are difficult to synchronize so that the proper valves open and close in precise timing with one another. If one opens or closes at an undesired time in relation to another solenoid valve, erratic action can result. This type of unpredictable behavior can be highly detrimental to the operation of an engine.
Another problem is that high pressure oil with varying viscosities, as is commonly found in a motor vehicle, can further complicate solenoid performance as far as speed of response. Oil condition can affect the separate solenoid control valves of the prior art valve actuators differently depending on several characteristics of the solenoid valve such as wear of the shut off device and the operating clearance.
Still another problem with prior art devices is their stability and ability to operate at a high duty cycle in the harsh environment found in a vehicle engine. Hot oil and heat conducted from the engine cylinder head commonly results in abnormally high operating temperatures which degrade the performance of prior art solenoid.